Retractable plasma torch for gasification reactors

ABSTRACT

An apparatus comprises: a gasifier vessel; an orifice in a wall of the gasifier vessel; a plasma torch; a torch support structure connected to the wall of the gasifier vessel and having an opening configured to receive the plasma torch, the torch support structure including a shroud gas spool configured to inject shroud gas into the opening and around the torch and an isolation valve configured to prevent gas flow between an internal environment of the gasifier and an external environment outside of the torch support structure when the plasma torch is retracted; and an actuator configured to extend the plasma torch into the gasifier vessel through the orifice and to retract the plasma torch from the gasifier vessel.

FIELD OF THE INVENTION

This invention relates to plasma torch assemblies, and moreparticularly, to such assemblies having retractable plasma torches thatcan be used with gasification reactors.

BACKGROUND

Plasma gasification reactors (sometimes referred to as PGRs) are a typeof pyrolytic reactor known and used for treatment of any of a wide rangeof materials including, for example, scrap metal, hazardous waste, othermunicipal or industrial waste and landfill material, and vegetativewaste or biomass to derive useful material, e.g., metals, or a synthesisgas (syngas), or to vitrify undesirable waste for easier disposition.

PGRs and their various uses are described in, for example, U.S. Pat. No.7,632,394 by Dighe et al., issued Dec. 15, 2009, titled “System andProcess for Upgrading Heavy Hydrocarbons”; U.S. Patent ApplicationPublication No. 2009/0307974 by Dighe et al., titled “System and Processfor Reduction of Greenhouse Gas and Conversion of Biomass”; U.S. PatentApplication Publication No. 2010/0199557 by Dighe et al., titled “PlasmaGasification Reactor”; and U.S. Patent Application PublicationUS2012/0199795 by Gorodetsky et al., titled “Enhanced Plasma Gasifiersfor Producing Syngas”, all of which are incorporated by reference hereinfor their descriptions of PGRs and methods practiced with them.

One manner of operating such a PGR is for gasifying material to producea syngas from a feed material. The feed material may include, asexamples, one or more of materials such as biomass, municipal solidwaste (MSW), coal, industrial waste, medical waste, hazardous waste,tires, and incinerator ash. In some installations, the PGR can producesyngas that contains useful amounts of hydrogen and carbon monoxide forsubsequent use as a fuel.

Heat from an electric arc can be fed into a cupola, furnace, or otherreactor vessel to enhance the operation thereof by providing a very hotgas stream which may be either oxidizing or reducing and can also bemixed with particulate material. The electric arc can be produced in aplasma torch in which the electric arc ionizes the gas which is blownout of the end of the torch, producing a hot gas stream which generallyoperates in the range of, for example, 10,000° F. (5,538° C.).

In various operating scenarios, it would be desirable to remove thetorch from the reactor vessel or to vary the position of the torch tochange the location of the hot gas stream within the reactor vessel.

SUMMARY

In one embodiment an apparatus includes a gasifier vessel; an orifice ina wall of the gasifier vessel; a plasma torch; a torch support structureconnected to the wall of the gasifier vessel and having an openingconfigured to receive the plasma torch, the torch support structureincluding a shroud gas spool configured to inject shroud gas into theopening and around the torch and an isolation valve configured toprevent gas flow between an internal environment of the gasifier and anexternal environment outside of the torch support structure when theplasma torch is retracted; and an actuator configured to extend theplasma torch into the gasifier vessel through the orifice and to retractthe plasma torch from the gasifier vessel.

In another embodiment, an apparatus includes: a gasifier vessel; anorifice in a wall of the gasifier vessel; a plasma torch; a torchsupport structure connected to the wall of the gasifier vessel andhaving an opening configured to receive the plasma torch, the torchsupport structure including an isolation valve configured to prevent gasflow between the internal environment of the gasifier and the externalenvironment outside of the torch support structure when the plasma torchis retracted, and a purge spool having first and second annular sealswith openings for receiving the plasma torch, with a plenum between thefirst and second annular seals to prevent gas flow between an internalenvironment of the gasifier and an external environment outside of thetorch support structure when the plasma torch is retracted but theisolation valve is not yet fully closed; and an actuator configured toextend the plasma torch into the gasifier vessel through the orifice andto retract the plasma torch from the gasifier vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is cross-sectional view of a retractable plasma torch assembly.

FIG. 2 is another cross-sectional view of the retractable plasma torchassembly of FIG. 1.

FIG. 3 is another cross-sectional view of the retractable plasma torchassembly of FIG. 1. FIG. 4 is a cross-sectional view of anotherretractable plasma torch assembly.

DETAILED DESCRIPTION

In one aspect, the present invention relates to plasma torch assembliesthat can be used in combination with a reactor vessel, such as agasification or vitrification reactor.

FIG. 1 is cross-sectional view of a retractable plasma torch assembly 10including a purged removal port apparatus 12 for a retractable plasmatorch 14. Components illustrated in FIG. 1 include a retractable plasmatorch 14 and a torch support structure 16. The torch support structure16 includes a shroud air spool 18, an isolation valve 20, and a purgegas spool 22. The assembly is shown in combination with a gasifiervessel 24 including a gasifier shell 26, a layer of refractory material28, a taphole 30, and a plasma torch nozzle 32 (also called a tuyere).In this simplified diagram, a number of components are omitted orsimplified in order to clearly highlight the functioning of the purgedremoval port apparatus 12.

With continued reference to FIG. 1, the plasma torch 14 is shown in theinstalled position, in which it can be operated as required (e.g. fortaphole heating) within the internal environment 34 of the gasifiervessel 24. The plasma torch 14 can be a water-cooled torch, and is shownto include a cylindrical portion that can be positioned along an axis 36of a generally cylindrical opening 38 in the torch support structure 16and the nozzle 32, using equipment such as an actuator 40. The actuator40 can be a linear actuator mechanism, for example, a piston, screw, orrack and pinion. In FIG. 1, the distal end 42 of the plasma torch 14 isshown to be embedded in a bed of process material 44. However, in otherembodiments, the distal end 42 of the plasma torch 14 need not beembedded in a bed of process material 44.

The torch support structure 16 is connected to the gasifier vessel 24.As shown in FIG. 1, the shroud air spool 18 is fixed to the plasma torchnozzle 32 and comprises a port 46 through which shroud air 48 (oralternatively, steam or oxygen-enriched air) can be supplied to protectcertain components of the plasma torch 14 and to focus a hot gas flow 50produced by the plasma torch 14. Under normal operation, shroud air 48is supplied at a pressure greater than the pressure within the internalenvironment 34, thereby preventing egress of syngas from the internalenvironment 34 through the plasma torch nozzle 32. A shroud airisolation valve 66 is fitted on the port 46 and is in the open positionto enable the supply of the shroud air 48 through the port 46. Theshroud air isolation valve 66 shown FIG. 1 is depicted as a slide gatetype, but could be any type of valve capable of achieving a gas-tightseal between the port 46 and an external environment 52.

Isolation valve 20, which could be any full port valve such as a slidegate or ball valve, is fixed between the shroud air spool 18 and thepurge gas spool 22. Isolation valve 20 may be closed to produce agas-tight seal between the internal environment 34 and the externalenvironment 52 in instances where the plasma torch 14 is removed formaintenance purposes. However, FIG. 1 depicts the plasma torch 14 in theinstalled position, so isolation valve 20 is in the open position.

Purge gas spool 22 includes a port 70 and annular sealing members 56, 58which are located annularly intermediate the plasma torch 14 and aninterior surface of the purge gas spool 22. The sealing members 56, 58may have a relatively snug fit between the plasma torch 14 and the purgegas spool 22 such that they cause a significant resistance to gas flowthrough the annular plenum between the plasma torch 14 and the purge gasspool 22. Between the sealing members 56, 58 is a purge gas plenum 60.The purge gas spool 22 is employed to prevent egress of syngas from theinterior environment 34 when the plasma torch 14 is removed formaintenance.

With continued reference to FIG. 1, it should be noted that the flange62 on the plasma torch 14 serves as a physical stop to prevent furtherpenetration of plasma torch 14 into the gasifier vessel 24. In otherapplications involving a fixed plasma torch, such a flange may beemployed for sealing purposes. However, in this embodiment, the plasmatorch 14 may be variably positioned during normal operation, so a sealbetween the internal environment 34 and the external environment 52 mustbe achieved by other means (i.e. through the shroud air sealingmechanism described above, and/or the purge gas sealing mechanismdescribed below), without the use of the flange 62.

FIG. 2 is another cross-sectional view of the retractable plasma torchassembly 10 of FIG. 1. In FIG. 2, plasma torch 14 is in the process ofbeing removed for maintenance and is offline. Shroud air flow throughthe shroud air spool 18 is turned off and isolation valve 20 is in theprocess of being closed, but is still at least partially open. In thisconfiguration, it is possible that syngas 64 from the interiorenvironment 34 could flow through the plasma torch nozzle 32 and pastthe open isolation valve 20. The shroud air isolation valve 66, nowshown in the fully closed position, is employed to prevent egress ofsyngas through the port 46 on the shroud air spool 18.

In the situation presented in FIG. 2, a flow of purge gas 68 (e.g.nitrogen) is supplied through port 70 and into the purge gas plenum 60.Due to the sealing action of the sealing members 56, 58, the flow ofpurge gas 68 will pressurize the purge gas plenum 60. If the pressurewithin the purge gas plenum 60 is maintained above the pressure of theinternal environment 34, any leakage across the sealing members 56, 58will only involve outflow of purge gas from the purge gas plenum 60 intothe internal environment 34 and the external environment 52. Leakage ofsyngas 64 across the sealing members 56, 58 and into the externalenvironment 52 would not be possible.

FIG. 3 is another cross-sectional view of the retractable plasma torchassembly 10 of FIG. 1 with the plasma torch 14 fully removed. Isolationvalve 20 is fully closed and achieves a gas-tight seal between theinternal environment 34 and the external environment 52, therebypreventing egress of any syngas 64.

It can be appreciated that the apparatus described above can also beemployed in a similar fashion to allow for re-insertion of the plasmatorch 14 into the plasma torch nozzle 32. It can also be understood thatthis apparatus does not require shutdown of the gasifier vessel 24, andthus enables “online” removal and re-insertion of the plasma torch 14.It should also be noted that variations on the above-described apparatusare possible, particularly those utilizing only one of either the purgegas spool 22 or the shroud air spool 18 for sealing under allconditions. For example, in an embodiment utilizing only the shroud airspool 18 (without the purge gas spool 22), the shroud air 48 (shown inFIG. 1) may be supplied at a sufficiently high pressure (i.e. a pressurehigher than the internal environment 34 and the external environment52), such that egress of any syngas 64 from the internal environment 34and ingress of any air from the external environment 52 is prevented,even in situations where the plasma torch 14 is fully removed and theisolation valve 20 is fully open. It can be understood that such anarrangement, while functional in terms of sealing, may require asignificantly greater supply of shroud air 48 compared to the embodimentdepicted in FIGS. 1-3, and may not be a preferred embodiment.

The embodiment of FIGS. 1-3 includes a water-cooled, retractable plasmatorch assembly 10 that includes an optional purged removal port (eitherthe shroud air spool 18 or the purge gas spool 22, as only one of thesecomponents would be required to ensure sealing under all conditions). Alinear actuator 40 (which could be hydraulic, pneumatic, electric, orother type) can be installed outside of the gasifier vessel 24 andserves to extend and retract the plasma torch 14.

A nozzle 32 serves as an orifice through which to extend/retract theplasma torch 14 within the gasifier vessel 24. The nozzle 32 can includerefractory lining where required for thermal protection. For example,the refractory lining 28 of the gasifier can extend into the nozzle asshown in FIGS. 1-3.

A build-up removal mechanism 72 can be included to remove any solidifiedslag build-up which may accumulate on the water-cooled surface of theplasma torch 14. In the embodiment of FIGS. 1-3, a mechanical rappingdevice is employed as the build-up removal mechanism 72. Alternativemechanisms, such as vibratory device or scraper, and mounted eitherwithin or external to the gasifier vessel, are also possible but notdepicted in FIGS. 1-3.

FIG. 4 is another cross-sectional view of a retractable plasma torchassembly 10 that includes many of the elements of FIGS. 1-3, and furtherincludes a scraper 74 mounted adjacent to the nozzle opening. In otherembodiment, multiple build-up removal mechanisms can be used, such asfor example both the mechanical rapping device 72 (shown in FIGS. 1 and2) and the scraper 74.

In various embodiments a plasma torch, configured to deliver a jet orplume of hot gas flow (also referred to as superheated gas flow) to achamber, is used in combination with a structure (i.e., the shroud inletassembly) that delivers a relatively cool gas (i.e. a shroud gas) aroundthe superheated gas stream. The shroud inlet assembly can deliver two ormore combinations of cold gas flow that surround the superheated gasflow. The shroud inlet assembly can be connected to a tubular or conicalchamber of a tuyere, with openings at either end, which transmits allgas flows to the process of the gasifier or furnace. The chamber can belined with a refractory material, and can be cooled by a fluid,potentially with a water jacket or a tubular cooling coil which can beembedded within the refractory material. The gas flow within the tuyerechamber can be directed in a way such that the superheated gas remainscentered and flowing along a central axis, with the shroud gases flowingbetween the superheated gas and the chamber wall.

Depending on the process design, internal pressure within the reactorvessel may be below atmospheric pressure (negative gauge pressure),above atmospheric pressure (positive gauge pressure), or approximatelyequal to atmospheric pressure (neutral pressure). Additionally, reactorvessels that normally operate at negative or neutral pressures may bedesigned to handle positive pressure excursions resulting from anomalousoperating conditions (e.g. introduction of water in the feed of a MSWgasifier). In the case of MSW gasifiers (which generate a gas mixturetermed “syngas”, comprising primarily H₂ and CO gas), a pressure seal isimportant for several reasons, including: prevention of air infiltrationinto the gasifier vessel, which could result in unwanted conversion ofcarbon or CO gas into CO₂ (by the introduction of oxygen from theambient air), as well as dilution of the syngas product (by theintroduction of nitrogen from the ambient air); and prevention of syngasegress into the external plant environment, which could pose a safetyhazard to plant personnel.

In reactor vessels such as municipal solid waste (MSW) gasifiers andelectric arc furnaces (EAFs), molten fluid (e.g. slag, metal) is removedthrough an opening in the vessel wall termed a “taphole”. Molten fluidexiting the taphole flows in a conduit (referred to as a “launder”) to acollection point for cooling, disposal, and/or further processing into asaleable product. This process is referred to as “tapping” and may beperformed on a continuous or batch basis.

In tapping processes, the taphole may be plugged, thereby preventingoutflow of molten fluid from the vessel. Taphole plugging may beintentional (e.g. injecting a clay into the taphole for batch tappingoperations) or may be unintentional (e.g. molten fluid from the vesselgradually solidifies within the taphole, causing a blockage). In eithercase, the taphole must eventually be unplugged to allow for furthertapping. Unplugging can be achieved by various means. One approachutilizes a plasma torch to melt through the plugged taphole from theexterior of the vessel. Generally, this approach to unplugging is knownas “lancing”. However, in some cases, external access to the taphole forthe purposes of plugging/unplugging may be considerably restricted byobstacles such as launders and slag granulation equipment. Additionally,some tapping operations may require manual operators in close proximityto the molten fluid, which presents a potential safety hazard. Theretractable torch assembly described herein can be used to enableunplugging of a taphole without external access to the taphole andwithout requiring manual operation in the vicinity of the taphole.

While particular aspects of the invention have been described above forpurposes of illustration, it will be evident to those skilled in the artthat numerous variations of the details of the present invention may bemade without departing from the invention as defined in the appendedclaims.

What is claimed is:
 1. An apparatus comprising: a gasifier vessel; anorifice in a wall of the gasifier vessel; a plasma torch; a torchsupport structure connected to the wall of the gasifier vessel andhaving an opening configured to receive the plasma torch, the torchsupport structure including a shroud gas spool configured to injectshroud gas into the opening and around the torch and an isolation valveconfigured to prevent gas flow between an internal environment of thegasifier and an external environment outside of the torch supportstructure when the plasma torch is retracted; and an actuator configuredto extend the plasma torch into the gasifier vessel through the orificeand to retract the plasma torch from the gasifier vessel.
 2. Theapparatus of claim 1, wherein the shroud gas spool is positioned betweenthe gasifier vessel and the isolation valve.
 3. The apparatus of claim1, further comprising: a build-up removal mechanism configured to removesolidified slag build-up on a surface of the plasma torch.
 4. Theapparatus of claim 3, wherein the build-up removal mechanism comprisesone or more of: a mechanical rapping device, a vibratory device, or ascraper.
 5. The apparatus of claim 4, wherein the scraper is mountedeither within or external to the gasifier vessel.
 6. The apparatus ofclaim 1, wherein the actuator comprises: a hydraulic actuator, apneumatic actuator, or an electric actuator.
 7. The apparatus of claim1, further comprising: a refractory lining adjacent to an inner surfaceof the orifice.
 8. The apparatus of claim 1, wherein the supportstructure further comprises: a purge spool including first and secondannular seals having openings for receiving the plasma torch, and aplenum between the first and second annular seals to prevent gas flowbetween the internal environment of the gasifier and the externalenvironment outside of the torch support structure when the plasma torchis retracted but the isolation valve is not yet fully closed.
 9. Theapparatus of claim 8, wherein the shroud gas spool is positioned betweenthe gasifier vessel and the isolation valve, and the isolation valve ispositioned between the shroud gas spool and the purge spool.
 10. Anapparatus comprising: a gasifier vessel; an orifice in a wall of thegasifier vessel; a plasma torch; a torch support structure connected tothe wall of the gasifier vessel and having an opening configured toreceive the plasma torch, the torch support structure including anisolation valve configured to prevent gas flow between the internalenvironment of the gasifier and the external environment outside of thetorch support structure when the plasma torch is retracted, and a purgespool having first and second annular seals with openings for receivingthe plasma torch, with a plenum between the first and second annularseals to prevent gas flow between an internal environment of thegasifier and an external environment outside of the torch supportstructure when the plasma torch is retracted but the isolation valve isnot yet fully closed; and an actuator configured to extend the plasmatorch into the gasifier vessel through the orifice and to retract theplasma torch from the gasifier vessel.
 11. The apparatus of claim 10,further comprising: a build-up removal mechanism configured to removesolidified slag build-up on a surface of the plasma torch.
 12. Theapparatus of claim 11, wherein the build-up removal mechanism comprises:a mechanical rapping device, a vibratory device, or a scraper.
 13. Theapparatus of claim 12, wherein the scraper is mounted either within orexternal to the gasifier vessel.
 14. The apparatus of claim 10, whereinthe actuator comprises: a hydraulic actuator, a pneumatic actuator, oran electric actuator.
 15. The apparatus of claim 10, further comprising:a refractory lining adjacent to an inner surface of the orifice.
 16. Theapparatus of claim 10, wherein the isolation valve is positioned betweenthe gasifier vessel and the purge spool.